Field of Invention
The present invention relates to an oil field perforation, and more particularly to a coaxial perforating charge and its perforation method for self-eliminating a compacted zone.
Description of Related Arts
Conventionally, during perforating and fracturing the oil well by the perforation fracture recombiner applied in the oil field, the recombinant explosive is detonated within the perforating gun and bursts the pressure-releasing holes which are pre-made in the perforating gun, so as to create a pressure within the well casing and further create a pressure on the stratum after the well pressure increased. Statistics indicate that the depth of the cement ring after the deep hole fracturing is around 800 mm, and the fracturing cracks are around 2500 mm; and calculations indicate that the energy of the perforation facture recombiner is mostly consumed within the well casing, which causes a big energy loss and an ordinary perforation and fracture performance. Besides, the perforation fracture recombiners widely adopted in the Chinese oil fields are usually equipped with the shaped charges. The shaped charge forms the perforated tunnel after perforation, but also induces a perforating compacted zone. The conventional jet perforation relies on the jet to squeeze and generate the holes, so it is inevitable to form the perforating compacted zone around the tunnel of the formed deep hole, which greatly decrease the permeability of the stratum. According to experiments, the mechanical property and the fluid flow performance of the rock within the compacted zone are damaged; the value of the permeability thereof remains only 10% of the original value. As a result, the compacted zone is the most important component of the perforation damage, and severely affects the oil well production capacity. The conventional shaped charge is unable to avoid the perforation compacted zone caused by the defect per se. The solution about the stratum perforating compacted zone is an international difficulty. It is an urge demand of the oil fields to eliminate the stratum perforating compacted zone.